BEIJING >> The death toll rose to 170 in the new virus outbreak in China on Thursday as foreign evacuees from the worst-hit region begin returning home under close observation and world health officials expressed “great concern” that the disease is starting to spread between people outside of China.

Thursday’s figures cover the previous 24 hours and represent an increase of 38 deaths and 1,737 cases for a total of 7,711. Of the new deaths, 37 were in the epicenter of the outbreak in Hubei province and one in the southwestern province of Sichuan.

The news comes as the 195 Americans evacuated from Wuhan, the Hubei province city of 11 million where the outbreak originated, are undergoing three days of testing and monitoring at a Southern California military base to make sure they do not show signs of the virus.

A group of 210 Japanese evacuees from Wuhan landed Thursday at Tokyo’s Haneda airport on a second government chartered flight, according to the foreign ministry. Reports said nine of those aboard the flight showed signs of cough and fever. Three of the 206 Japanese who returned on Wednesday tested positive for the new coronavirus, Prime Minister Shinzo Abe said during a parliamentary session.

France, New Zealand, Australia and other countries are also pulling out their citizens or making plans to do so.

World Health Organization emergencies chief said the few cases of human-to-human spread of the virus outside China — in Japan, Germany, Canada and Vietnam — were of “great concern” and were part of the reason the U.N. health agency’s director-general was reconvening a committee of experts on Thursday to assess whether the outbreak should be declared a global emergency.

The new virus has now infected more people in China than were sickened there during the 2002-2003 SARS outbreak.

Dr. Michael Ryan spoke at a news conference in Geneva on Wednesday after returning from a trip to Beijing to meet with Chinese President Xi Jinping and other senior government leaders. He said China was taking “extraordinary measures in the face of an extraordinary challenge” posed by the outbreak.

To date, about 99% of the cases are in China. Ryan estimated the death rate of the new virus at 2%, but said the figure was very preliminary. With fluctuating numbers of cases and deaths, scientists are only able to produce a rough estimate of the fatality rate and it’s likely many milder cases of the virus are being missed.

In comparison, the SARS virus killed about 10% of people who caught it. The new virus is from the coronavirus family, which includes those that can cause the common cold as well as more serious illnesses such as SARS and MERS.

Scientists say there are many questions to be answered about the new virus, including just how easily it spreads and how severe it is.

In a report published Wednesday, Chinese researchers suggested that person-to-person spread among close contacts occurred as early as mid-December.

“Considerable efforts” will be needed to control the spread if this ratio holds up elsewhere, researchers wrote in the report, published in the New England Journal of Medicine.

More than half of the cases in which symptoms began before Jan. 1 were tied to a seafood market, but only 8% of cases after that have been, researchers found. They reported the average incubation period was five days.

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Countries began evacuating their citizens Wednesday from the Chinese city hardest-hit by a new virus that has now infected more people in China than were sickened in the country by SARS.

The number of confirmed cases jumped to 5,974, surpassing the 5,327 in mainland China during the SARS outbreak in 2002-2003.

The death toll rose to 132, which is still lower than the 348 people who were killed in China by SARS, or severe acute respiratory syndrome. Scientists say there are still many questions to be answered about the new virus, including just how transmissible and severe it is.

Chartered planes carrying about 200 evacuees each arrived in Japan and the United States early Wednesday as other countries planned similar evacuations from the city of Wuhan, which authorities have shut down to try to contain the virus.

The first cases in the Middle East were confirmed Wednesday, a family of four from Wuhan that was visiting the United Arab Emirates. Airlines around the world announced they were cutting flights to China, and Hong Kong was suspending rail travel to and from the mainland at midnight.

The number of cases in China rose 1,459 from the previous day, a smaller increase than the 1,771 new cases reported Tuesday. Australia and Singapore were among those reporting new cases, as the number outside China topped 70. The vast majority are people who came from Wuhan.

Four passengers on the evacuation flight to Japan had coughs and fevers, and two were diagnosed with pneumonia.

It wasn’t clear whether they were infected with the new virus, which first appeared in Wuhan in December. Its symptoms, including cough and fever and in severe cases pneumonia, are similar to many other illnesses.

Takeo Aoyama, an employee at Nippon Steel Corp.’s subsidiary in Wuhan, told reporters he was relieved to be able to return home.

“We were feeling increasingly uneasy as the situation developed so rapidly and we were still in the city,” Aoyama said, his voice muffled by a white surgical mask.

The U.S. plane was headed to California after a refueling stop in Alaska. All 201 passengers, who included diplomats from the U.S. Consulate in Wuhan, passed health screenings in China and Anchorage.

Australia, New Zealand and Britain were among the latest countries to announce they are planning evacuations.

British Airways said it was suspending all flights to and from mainland China after the U.K. government warned against unnecessary travel to the country. The airline has daily flights from London to Shanghai and Beijing.

British health secretary Matt Hancock tweeted that “anyone who returns from Wuhan will be safely isolated for 14 days, with all necessary medical attention.” The measures are a step up from those during the devastating 2014-16 Ebola outbreak, when returning travelers from West Africa were asked to monitor themselves for symptoms.

Mark Woolhouse, a professor of infectious disease epidemiology at the University of Edinburgh, said the steps are justified to prevent the introduction of the virus and its spread.

“There’s always a balance between the draconian measures of public health and what people might want to do, and obviously it’s regrettable if people who turn out not to have the virus are quarantined unnecessarily,” he said.

The outbreak has affected international sporting events. The International Hockey Federation postponed Pro League games in China, and soccer, basketball and boxing qualifiers for the Tokyo Olympics in February have been moved outside of the country.

In Australia, health officials said the Chinese women’s national soccer team was quarantined in the city of Brisbane because it had passed through Wuhan a week ago.

The team will be kept in isolation in a hotel until Jan. 5. None of the 32 players and staff have shown symptoms.

In China’s Hubei province, 17 cities including Wuhan have been locked down, trapping more than 50 million people in the most far-reaching disease control measures ever imposed.

Sara Platto, an Italian animal behavior researcher and veterinarian, said there were 25 Italians stuck in Wuhan, who stay in touch online for material and emotional support.

“My son turned 12 on January 23, the first day of the lockdown in Wuhan. So he couldn’t invite his friends over. We had a remote birthday celebration, with people ‘visiting’ him over WeChat,” Platto said, referring to a Chinese messaging app. “We called it the epidemic birthday.”

As much as panic, people spending most of their time indoors have to deal with boredom.

Her son Matteo usually has a very busy agenda between his school, sports, and volunteer work, but now “it’s like suddenly everything has slowed down,” Platto said. As with other international schools, classes are moving online until the all-clear is sounded.

The new virus is from the coronavirus family, which includes those that can cause the common cold as well as more serious illnesses such as SARS and MERS. As of December, MERS had sickened nearly 2,500 people since its identification in 2012.

The source of the new virus and the full extent of its spread are still unknown. However, the World Health Organization said most cases reported to date “have been milder, with around 20% of those infected experiencing severe illness.”

Scientists expect many crucial questions about the virus’ behavior will be answered in the coming weeks as the outbreak evolves and it becomes clearer how people are infected.

Although the Chinese health minister and others have suggested that the virus is spreading before people get symptoms, data to confirm that has not yet been shared widely beyond China.

“It’s still unclear whether that takes place,” said Malik Peiris, chair in virology at the University of Hong Kong.

If it does, that might explain why China has already exceeded the case numbers for SARS.

“The fortunate thing about SARS, if there was anything fortunate, was that transmission did not take place before symptoms,” he said. Peiris said that if it turns out that the new coronavirus can indeed be spread by people who don’t show any symptoms, “a pandemic is a scenario that we have to consider.”